1. Field of the Invention
The present invention relates to an electroluminescent module comprising an electroluminescent element as combined with an circuit board, etc.
2. Description of the Related Art
An electroluminescent element comprises a transparent electrode layer of ITO as formed on the back surface of a transparent electrode film that is positioned in the front, in which a light-emitting layer, a dielectric layer and a back electrode layer are formed in that order on the back surface of the transparent electrode layer. With that constitution, an electroluminescent element is electrically connected with a circuit board, on which is mounted the electroluminescent element or a driving circuit for a portable electronic appliance as connected with the electroluminescent element, by connecting each electrode part of the transparent electrode layer and the back electrode layer of the electroluminescent element with the circuit pattern or the flexible print cable (FPC) as formed on the circuit board.
Integrating an electroluminescent element with a circuit board or the like in the manner mentioned above gives an electroluminescent module, which is built in various electronic appliances. For example, an electroluminescent element is much used as the backlight for the switch key and the display part of portable telephones, in which an electroluminescent element is fitted to and electrically connected with a circuit board provided with a driving circuit in such a manner that the electrode parts of the electroluminescent element are connected with the connecting pattern of the circuit board.
FIG. 3A and FIG. 3B show interconnection structures of the electrode parts of a conventional electroluminescent module. In FIG. 3A, the electrode part 43a is in the side of the transparent electrode layer. In FIG. 3B, the electrode part 43b is in the side of the back electrode layer. In those, the front of the circuit board 41 (upper surface in FIG. 3A and FIG. 3B) is provided with a connecting pattern (not shown), and an electroluminescent element is fitted thereto via a conductive adhesive 42a. On the back surface of the transparent electrode film 44 of the electroluminescent element, formed is a transparent electrode layer 45. In the part that is to be the electrode part 43a, a conductive layer 46 is formed on the back surface of the transparent electrode layer 45. While pressing a hot iron against the electrode part 43a, the connecting pattern is electrically connected with the transparent electrode layer 45 via the conductive adhesive 42a. 
FIG. 3B shows the electrode part 43b in the side of the back electrode layer. In this, an electroluminescent element is fitted under pressure to the connecting pattern as formed on the circuit board 41 in a position different from that of the electrode part 43a in the side of the transparent electrode layer, via a conductive adhesive 42b. The electroluminescent element comprises a light-emitting layer 47, a dielectric layer 48 and a back electrode layer 49 as formed on the back surface of the transparent electrode layer 45 formed on the back surface of the transparent electrode film 44. In the region to be the connecting electrode part, the light-emitting layer 47 is not formed. In that region, formed is a dielectric layer 48 to fill it, by which the contact of the transparent electrode layer 45 with the back electrode layer 49 is blocked. Under thermal pressure, the connecting pattern is electrically connected with the back electrode layer 49 via the conductive adhesive 42b therebetween.
As mentioned hereinabove, when each electrode part is connected with the connecting pattern under thermal pressure, the part against which a hot iron for thermal pressure is pressed is heated at high temperature of 160 C or higher. Therefore, that part thus heated under pressure shall receive residual peeling stress and external peeling force, whereby the electrode part in the side of the transparent electrode layer will be cracked or the transparent electrode layer and the electrode part will be delaminated at the boundary therebetween. Such cracking and delamination will often cause electrical interconnection failure. Also in the electrode part in the side of the back electrode layer, the transparent electrode layer and the back electrode layer will be delaminated at the boundary therebetween owing to the residual peeling stress and the external peeling force.
In the related art, the position at which the electroluminescent element is fitted to the circuit board differs from that at which each electrode part is connected with the circuit pattern, which, however, requires different steps for the fitting and the connection in different positions, thereby causing the increase in the production costs. In that, in addition, since the electrode interconnection area differs from the electroluminescent element-fitting area, a large space is needed for those areas, and the electroluminescent element fitting to the circuit board could not be well balanced with the electrode interconnection on the board. This brings about still another problem in that the fitting of the electroluminescent element to the circuit board is often unstable.
To solve the problems noted above, the electroluminescent module of the invention comprises an electroluminescent element as electrically connected with a circuit board on which is mounted the electroluminescent element or a driving circuit for a portable electronic appliance as connected with the electroluminescent element, and is characterized in that the connecting electrode part in the side of the transparent electrode layer and the connecting electrode part in the side of the back electrode layer are provided in the facing opposite sides of the electroluminescent element, and that the electroluminescent element is electrically connected with the circuit board via the connecting electrode parts by bonding it to the circuit board at those parts. With that constitution, the electroluminescent module of the invention saves any superfluous space of the circuit board to which the electroluminescent element is bonded.
In the electroluminescent module of the invention, a flexible, insulating resin layer is provided in two separate sites both adjacent to the transparent electrode layer in such a manner that the connecting electrode part to be electrically connected with the transparent electrode layer is provided on one insulating resin layer while the connecting electrode part to be electrically connected with the back electrode layer is provided on the other insulating resin layer. In this, these insulating resin layers are to absorb the residual peeling stress and the external peeling force applied to the boundary between the connecting pattern of the circuit board and each connecting electrode of the electroluminescent element so as to prevent the delamination at their boundary, thereby improving the quality of the electroluminescent module.